Atherosclerosis is a progressive disease of the vascular system whereby atheroma is deposited on the inner walls of blood vessels. Atherosclerosis is a complex, progressive and degenerative condition resulting in the build-up of cholesterol and other obstructive materials, known as plaque, on the walls of the arteries. The accumulation of plaque narrows the interior or lumen of arteries, thereby reducing blood flow.
Plaque occurs in the arteries in several different forms and may be located in many different anatomies throughout the arterial system. Plaque varies in composition, with portions that are hard and brittle, referred to as calcified plaque, and other portions that are fatty or fibrous. Over time atheromatous deposits can become large enough to reduce or occlude blood flow through the vessels, leading to symptoms of low blood flow, such as pain in the legs (on walking or at rest), skin ulcer, angina (at rest or exertional), and other symptoms. To treat this disease and improve or resolve these symptoms it is desirable to restore or improve blood flow through the vessel.
Various means are used to restore or improve blood flow through atheromatous vessels. The atheroma deposits can be displaced by diametrically expanding the vessel by inflating balloons, expanding stents, and other methods. Such scar tissue (restenotic material), once formed, blocks flow in the vessel and often needs to be removed. The deposits can be pulverized using lasers and other methods however pulverization alone of atheromatous material may allow microemboli to flow downstream and lodge in distal vascular beds, further compromising blood flow to the tissue affected by the disease. Atherectomy catheters can be used to remove atheromatous deposits from the blood vessel and can present an ideal solution when the atheromatous debris removed from the vessel is captured and removed from the body.
Many types of atherectomy catheter devices have been proposed, including catheters with rotating burrs, lasers to photo-dissolve tissue, and catheters which use balloons or other positioning devices to position the cutter adjacent material to be removed.
Additionally, some catheters have a collection chamber positioned distally of the cutting window. This requires that the length of the catheter distal of the cutting window be long enough to accommodate the collection chamber. This creates some conflicting design choices. On the one hand, it is desirable for the collection chamber to have a capacity large enough to accommodate a reasonable amount of cut material before the chamber fills and the catheter must be removed. On the other hand, the increased length of the catheter distal to the cutting window necessary to accommodate a sufficiently large collection chamber is disadvantageous in certain applications. For example, if the treatment site or lesion is located in a vessel with a particularly tortuous anatomy or small size there might not be enough accessible vessel space distal to the lesion to accommodate the distal length of the catheter distal of the cutting window. This accessible space distal to the treatment site is sometimes referred to as the “landing zone”. In order for the catheter to be used effectively the anatomy of the vessel must be such as to enable the catheter to be advanced far enough to position the cutting window within the treatment site and the distal portion of the catheter, which houses the collection chamber, in the landing zone. Thus, catheters having collection chambers located distally of the cutting window might be difficult to use in vessels with short landing zones.
In U.S. Provisional Patent Application 61/354,487 filed Jun. 14, 2010, the contents of which are incorporated herein by reference in their entirety, an atherectomy catheter which overcomes some of these problems is disclosed. The catheter has a rotating distal tip with an abrasive surface enabling the catheter to cut through and cross a CTO. The catheter includes a side cutting window and a cutting blade configured to extend through the window to cut material from the wall of a vessel at a treatment site as the catheter is pulled proximally through the treatment site. The catheter includes a material collection chamber which is positioned proximally of the cutting window. During use the rotating abrasive tip enables the catheter to cross a treatment site even if it is a CTO. The cutting window is advanced distal to the treatment site, the cutting blade is extended out the window and material is cut from the treatment site by pulling the catheter proximally across the treatment site. Since the material collection chamber is located proximal of the cutting window the length of the catheter distal to the cutting window is reduced enabling the catheter to treat lesions having short landing zones.
Although this catheter has features which overcome some of the problems described above there continues to be a need for an atherectomy catheter which can be used to access and treat lesions in the vasculature, even if the lesions are in locations which are difficult to treat with prior art catheters and even if the vessels are totally occluded at the treatment site. Further, there is need for an atherectomy catheter which is configured to efficiently transport cut debris from the location of cutting to a location of storage, even if the storage location is proximally spaced from the cutting location.